1. Field of the Invention
The invention relates to cavitation enhanced liquid atomization. More particularly, the invention relates to atomizing a fluid comprising a solution of the liquid to be atomized and a lower boiling cavitation liquid, by contacting the fluid under pressure and while flowing, with a pressure reducing means to reduce the fluid pressure and thereby produce nucleation and growth of bubbles comprising vapor of the cavitation liquid in the fluid, at a temperature below the bubble point of the solution, and then passing the fluid through an atomizing means into a lower pressure atomizing zone. Bubble nucleation is induced upstream of the atomizing means. This is useful for atomizing a hot FCC feed oil into a catalytic cracking reaction zone, using a lower boiling hydrocarbon as the cavitation liquid.
2. Background of the Invention
Fluid atomization is well known and used in a wide variety of applications and processes. These include, for example, aerosol sprays, the application of pesticides and coatings, spray drying, humidification, mixing, air conditioning, and chemical and petroleum refinery processes. For most applications, a fluid under pressure, with or without the assistance of an atomizing gas, is forced through a pressure reducing orifice in an atomization nozzle. Atomization occurs as the fluid passes through the orifice and into the lower pressure zone downstream. The degree of atomization is determined by the orifice size, the pressure drop across the orifice, fluid density, viscosity, and surface tension, etc., as is known. Atomization is increased and the droplet size is decreased, with decreasing orifice size and increasing pressure drop. Atomizing relatively viscous fluids at high flow rates, such as the heavy petroleum oil feeds used in fluidized catalytic cracking (FCC) processes, or fluid cat cracking as it is also called, is particularly challenging. FCC is an established and widely used process in the petroleum refining industry, primarily for converting high boiling petroleum oils to more valuable lower boiling products, including gasoline and middle distillates such as kerosene, jet and diesel fuel, and heating oil. In an FCC process, the preheated oil feed is mixed with steam or a low molecular weight (e.g., C.sub.4-) gas under pressure, to form a two phase, gas and liquid fluid. This fluid is passed through a pressure-reducing orifice into a lower pressure atomization zone, in which the gas expands and the oil is atomized, and brought into contact with a particulate, hot cracking catalyst. The atomization is effected primarily by the shearing action between the gas and liquid phases, as the fluid passes through the orifice and into the lower pressure atomization zone. The FCC riser comprises both the feed atomization zone and the cat cracking zone. Steam is more often used than a light hydrocarbon gas, to reduce the vapor loading on the on the gas compression facilities and the downstream products fractionation. However, the use of steam produces sour water, which enhances corrosion. Sour water is also environmentally unfriendly and must therefore be treated before disposal. There is a need therefore, for a process that either reduces or eliminates the amount of steam or low molecular weight gas atomizing agents.